Just looked it up. I'd been confusing it with Who Can Kill a Child? which I wouldn't classify as a masterpiece by any stretch of the imagination. I've not seen it - I'll give it a look.
And a couple of reels of rushes from an unfinished Karloff movie...
And string. Lots of string and Gaffer tape.
Make no mistake, the first half is in the 'so bad it's good' genre, then quite unexpectedly turns believable (beer goggles recommended).